CVE-2025-29946: SEV Firmware IOMMU Flush Vulnerability

CVE-2025-29946 Overview

CVE-2025-29946 is a firmware vulnerability in AMD Secure Encrypted Virtualization (SEV) technology where insufficient or incomplete data removal in the hardware component results in the IOMMU not being fully flushed. This flaw can potentially lead to a loss of confidentiality and integrity in guest virtual machine memory, allowing attackers with local privileged access to potentially access or modify sensitive data in guest environments.

Critical Impact

This vulnerability affects the security guarantees of AMD SEV technology, potentially compromising the isolation between guest virtual machines and the hypervisor layer by allowing incomplete IOMMU state transitions.

Affected Products

• AMD SEV-enabled processors with vulnerable firmware
• Systems utilizing AMD Secure Encrypted Virtualization technology
• Virtualization environments relying on SEV for guest memory protection

Discovery Timeline

• 2026-02-10 - CVE CVE-2025-29946 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2025-29946

Vulnerability Analysis

This vulnerability falls under CWE-1301 (Insufficient or Incomplete Data Removal Within Hardware Component). The core issue lies in the SEV firmware's handling of the Input/Output Memory Management Unit (IOMMU) during certain state transitions. When the IOMMU flush operation is triggered, the firmware fails to completely clear residual data from hardware buffers.

AMD's Secure Encrypted Virtualization (SEV) technology is designed to isolate virtual machine memory from the hypervisor and other guests by encrypting it with unique keys. The IOMMU plays a critical role in this architecture by controlling device access to physical memory. When the IOMMU is not fully flushed, residual address translation entries or DMA mappings may persist, creating a window where guest memory isolation guarantees are violated.

The attack requires local access with high privileges (such as hypervisor-level access) and depends on specific timing conditions, making exploitation complex but not impossible in targeted attack scenarios.

Root Cause

The root cause stems from incomplete data removal logic within the SEV firmware's IOMMU management routines. During certain operations that require clearing IOMMU state—such as guest VM teardown, migration, or security context changes—the firmware's flush mechanism does not account for all hardware caches and translation lookaside buffers (TLBs) associated with the IOMMU.

This incomplete removal can leave stale entries that map to guest physical memory addresses, potentially allowing subsequent operations to access memory regions that should have been invalidated and protected.

Attack Vector

An attacker with local privileged access (typically at the hypervisor or firmware level) could exploit this vulnerability by:

1. Triggering operations that cause the SEV firmware to flush IOMMU state
2. Exploiting the race condition window where residual data remains in hardware buffers
3. Using the stale IOMMU mappings to read or write guest VM memory that should be protected

The attack requires precise timing and deep knowledge of the hardware architecture, making it a sophisticated attack that would likely be employed in targeted scenarios against high-value virtualization environments.

The vulnerability mechanism involves the IOMMU's translation lookaside buffer (TLB) not being properly invalidated during flush operations. When a guest VM's memory context should be completely isolated, residual TLB entries may still permit DMA operations to access memory regions. See the AMD Security Bulletin AMD-SB-3023 for detailed technical information.

Detection Methods for CVE-2025-29946

Indicators of Compromise

• Unexpected DMA operations targeting guest VM memory regions after context switches
• Anomalous IOMMU fault logs indicating access to invalidated memory mappings
• Irregular behavior in guest VM memory integrity checks
• Unusual patterns in hypervisor memory access auditing

Detection Strategies

• Monitor IOMMU fault registers for unexpected access attempts to protected memory regions
• Implement firmware integrity verification to ensure SEV firmware hasn't been tampered with
• Enable verbose IOMMU logging to capture translation failures and access anomalies
• Utilize hardware security monitoring tools that can detect improper memory isolation states

Monitoring Recommendations

• Enable and regularly review IOMMU event logs for suspicious access patterns
• Implement host-based intrusion detection focused on hypervisor-level anomalies
• Monitor for unusual firmware update attempts or configuration changes
• Deploy SentinelOne Singularity Platform for comprehensive endpoint protection and real-time threat detection in virtualized environments

How to Mitigate CVE-2025-29946

Immediate Actions Required

• Review the AMD Security Bulletin AMD-SB-3023 for specific guidance
• Inventory all systems using AMD SEV technology to determine exposure
• Prioritize firmware updates for systems hosting sensitive workloads
• Implement additional access controls to restrict hypervisor-level access

Patch Information

AMD has released updated SEV firmware to address this vulnerability. System administrators should consult the AMD Security Bulletin AMD-SB-3023 for specific firmware versions and update instructions. Coordinate with your hardware vendor or server manufacturer for platform-specific firmware update packages.

Workarounds

• Restrict administrative and hypervisor-level access to trusted personnel only
• Implement network segmentation to limit exposure of virtualization management interfaces
• Consider disabling SEV features on non-critical workloads until patches are applied
• Enable enhanced auditing of privileged operations in the virtualization environment

# Configuration example
# Check current SEV firmware version (Linux)
dmesg | grep -i "sev"
# Verify IOMMU status
cat /sys/kernel/iommu_groups/*/type
# Review AMD SEV capabilities
cat /sys/module/kvm_amd/parameters/sev